/*
 * Copyright (C) 2016 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package androidx.media3.container;

import static java.lang.Math.min;

import androidx.annotation.Nullable;
import androidx.media3.common.C;
import androidx.media3.common.ColorInfo;
import androidx.media3.common.Format;
import androidx.media3.common.MimeTypes;
import androidx.media3.common.util.Assertions;
import androidx.media3.common.util.Log;
import androidx.media3.common.util.UnstableApi;
import java.nio.ByteBuffer;
import java.util.Arrays;

/** Utility methods for handling H.264/AVC and H.265/HEVC NAL units. */
@UnstableApi
public final class NalUnitUtil {

  private static final String TAG = "NalUnitUtil";

  /** Coded slice of a non-IDR picture. */
  public static final int NAL_UNIT_TYPE_NON_IDR = 1;

  /** Coded slice data partition A. */
  public static final int NAL_UNIT_TYPE_PARTITION_A = 2;

  /** Coded slice of an IDR picture. */
  public static final int NAL_UNIT_TYPE_IDR = 5;

  /** Supplemental enhancement information. */
  public static final int NAL_UNIT_TYPE_SEI = 6;

  /** Sequence parameter set. */
  public static final int NAL_UNIT_TYPE_SPS = 7;

  /** Picture parameter set. */
  public static final int NAL_UNIT_TYPE_PPS = 8;

  /** Access unit delimiter. */
  public static final int NAL_UNIT_TYPE_AUD = 9;

  /** Prefix NAL unit. */
  public static final int NAL_UNIT_TYPE_PREFIX = 14;

  /** Holds data parsed from a H.264 sequence parameter set NAL unit. */
  public static final class SpsData {

    public final int profileIdc;
    public final int constraintsFlagsAndReservedZero2Bits;
    public final int levelIdc;
    public final int seqParameterSetId;
    public final int maxNumRefFrames;
    public final int width;
    public final int height;
    public final float pixelWidthHeightRatio;
    public final int bitDepthLumaMinus8;
    public final int bitDepthChromaMinus8;
    public final boolean separateColorPlaneFlag;
    public final boolean frameMbsOnlyFlag;
    public final int frameNumLength;
    public final int picOrderCountType;
    public final int picOrderCntLsbLength;
    public final boolean deltaPicOrderAlwaysZeroFlag;
    public final @C.ColorSpace int colorSpace;
    public final @C.ColorRange int colorRange;
    public final @C.ColorTransfer int colorTransfer;

    public SpsData(
        int profileIdc,
        int constraintsFlagsAndReservedZero2Bits,
        int levelIdc,
        int seqParameterSetId,
        int maxNumRefFrames,
        int width,
        int height,
        float pixelWidthHeightRatio,
        int bitDepthLumaMinus8,
        int bitDepthChromaMinus8,
        boolean separateColorPlaneFlag,
        boolean frameMbsOnlyFlag,
        int frameNumLength,
        int picOrderCountType,
        int picOrderCntLsbLength,
        boolean deltaPicOrderAlwaysZeroFlag,
        @C.ColorSpace int colorSpace,
        @C.ColorRange int colorRange,
        @C.ColorTransfer int colorTransfer) {
      this.profileIdc = profileIdc;
      this.constraintsFlagsAndReservedZero2Bits = constraintsFlagsAndReservedZero2Bits;
      this.levelIdc = levelIdc;
      this.seqParameterSetId = seqParameterSetId;
      this.maxNumRefFrames = maxNumRefFrames;
      this.width = width;
      this.height = height;
      this.pixelWidthHeightRatio = pixelWidthHeightRatio;
      this.bitDepthLumaMinus8 = bitDepthLumaMinus8;
      this.bitDepthChromaMinus8 = bitDepthChromaMinus8;
      this.separateColorPlaneFlag = separateColorPlaneFlag;
      this.frameMbsOnlyFlag = frameMbsOnlyFlag;
      this.frameNumLength = frameNumLength;
      this.picOrderCountType = picOrderCountType;
      this.picOrderCntLsbLength = picOrderCntLsbLength;
      this.deltaPicOrderAlwaysZeroFlag = deltaPicOrderAlwaysZeroFlag;
      this.colorSpace = colorSpace;
      this.colorRange = colorRange;
      this.colorTransfer = colorTransfer;
    }
  }

  /** Holds data parsed from a H.265 sequence parameter set NAL unit. */
  public static final class H265SpsData {

    public final int generalProfileSpace;
    public final boolean generalTierFlag;
    public final int generalProfileIdc;
    public final int generalProfileCompatibilityFlags;
    public final int chromaFormatIdc;
    public final int bitDepthLumaMinus8;
    public final int bitDepthChromaMinus8;
    public final int[] constraintBytes;
    public final int generalLevelIdc;
    public final int seqParameterSetId;
    public final int width;
    public final int height;
    public final float pixelWidthHeightRatio;
    public final @C.ColorSpace int colorSpace;
    public final @C.ColorRange int colorRange;
    public final @C.ColorTransfer int colorTransfer;

    public H265SpsData(
        int generalProfileSpace,
        boolean generalTierFlag,
        int generalProfileIdc,
        int generalProfileCompatibilityFlags,
        int chromaFormatIdc,
        int bitDepthLumaMinus8,
        int bitDepthChromaMinus8,
        int[] constraintBytes,
        int generalLevelIdc,
        int seqParameterSetId,
        int width,
        int height,
        float pixelWidthHeightRatio,
        @C.ColorSpace int colorSpace,
        @C.ColorRange int colorRange,
        @C.ColorTransfer int colorTransfer) {
      this.generalProfileSpace = generalProfileSpace;
      this.generalTierFlag = generalTierFlag;
      this.generalProfileIdc = generalProfileIdc;
      this.generalProfileCompatibilityFlags = generalProfileCompatibilityFlags;
      this.chromaFormatIdc = chromaFormatIdc;
      this.bitDepthLumaMinus8 = bitDepthLumaMinus8;
      this.bitDepthChromaMinus8 = bitDepthChromaMinus8;
      this.constraintBytes = constraintBytes;
      this.generalLevelIdc = generalLevelIdc;
      this.seqParameterSetId = seqParameterSetId;
      this.width = width;
      this.height = height;
      this.pixelWidthHeightRatio = pixelWidthHeightRatio;
      this.colorSpace = colorSpace;
      this.colorRange = colorRange;
      this.colorTransfer = colorTransfer;
    }
  }

  /** Holds data parsed from a picture parameter set NAL unit. */
  public static final class PpsData {

    public final int picParameterSetId;
    public final int seqParameterSetId;
    public final boolean bottomFieldPicOrderInFramePresentFlag;

    public PpsData(
        int picParameterSetId,
        int seqParameterSetId,
        boolean bottomFieldPicOrderInFramePresentFlag) {
      this.picParameterSetId = picParameterSetId;
      this.seqParameterSetId = seqParameterSetId;
      this.bottomFieldPicOrderInFramePresentFlag = bottomFieldPicOrderInFramePresentFlag;
    }
  }

  /** Four initial bytes that must prefix NAL units for decoding. */
  public static final byte[] NAL_START_CODE = new byte[] {0, 0, 0, 1};

  /** Value for aspect_ratio_idc indicating an extended aspect ratio, in H.264 and H.265 SPSs. */
  public static final int EXTENDED_SAR = 0xFF;

  /** Aspect ratios indexed by aspect_ratio_idc, in H.264 and H.265 SPSs. */
  public static final float[] ASPECT_RATIO_IDC_VALUES =
      new float[] {
        1f /* Unspecified. Assume square */,
        1f,
        12f / 11f,
        10f / 11f,
        16f / 11f,
        40f / 33f,
        24f / 11f,
        20f / 11f,
        32f / 11f,
        80f / 33f,
        18f / 11f,
        15f / 11f,
        64f / 33f,
        160f / 99f,
        4f / 3f,
        3f / 2f,
        2f
      };

  private static final int H264_NAL_UNIT_TYPE_SEI = 6; // Supplemental enhancement information
  private static final int H264_NAL_UNIT_TYPE_SPS = 7; // Sequence parameter set
  private static final int H265_NAL_UNIT_TYPE_PREFIX_SEI = 39;

  private static final Object scratchEscapePositionsLock = new Object();

  /**
   * Temporary store for positions of escape codes in {@link #unescapeStream(byte[], int)}. Guarded
   * by {@link #scratchEscapePositionsLock}.
   */
  private static int[] scratchEscapePositions = new int[10];

  /**
   * Unescapes {@code data} up to the specified limit, replacing occurrences of [0, 0, 3] with [0,
   * 0]. The unescaped data is returned in-place, with the return value indicating its length.
   *
   * <p>Executions of this method are mutually exclusive, so it should not be called with very large
   * buffers.
   *
   * @param data The data to unescape.
   * @param limit The limit (exclusive) of the data to unescape.
   * @return The length of the unescaped data.
   */
  public static int unescapeStream(byte[] data, int limit) {
    synchronized (scratchEscapePositionsLock) {
      int position = 0;
      int scratchEscapeCount = 0;
      while (position < limit) {
        position = findNextUnescapeIndex(data, position, limit);
        if (position < limit) {
          if (scratchEscapePositions.length <= scratchEscapeCount) {
            // Grow scratchEscapePositions to hold a larger number of positions.
            scratchEscapePositions =
                Arrays.copyOf(scratchEscapePositions, scratchEscapePositions.length * 2);
          }
          scratchEscapePositions[scratchEscapeCount++] = position;
          position += 3;
        }
      }

      int unescapedLength = limit - scratchEscapeCount;
      int escapedPosition = 0; // The position being read from.
      int unescapedPosition = 0; // The position being written to.
      for (int i = 0; i < scratchEscapeCount; i++) {
        int nextEscapePosition = scratchEscapePositions[i];
        int copyLength = nextEscapePosition - escapedPosition;
        System.arraycopy(data, escapedPosition, data, unescapedPosition, copyLength);
        unescapedPosition += copyLength;
        data[unescapedPosition++] = 0;
        data[unescapedPosition++] = 0;
        escapedPosition += copyLength + 3;
      }

      int remainingLength = unescapedLength - unescapedPosition;
      System.arraycopy(data, escapedPosition, data, unescapedPosition, remainingLength);
      return unescapedLength;
    }
  }

  /**
   * Discards data from the buffer up to the first SPS, where {@code data.position()} is interpreted
   * as the length of the buffer.
   *
   * <p>When the method returns, {@code data.position()} will contain the new length of the buffer.
   * If the buffer is not empty it is guaranteed to start with an SPS.
   *
   * @param data Buffer containing start code delimited NAL units.
   */
  public static void discardToSps(ByteBuffer data) {
    int length = data.position();
    int consecutiveZeros = 0;
    int offset = 0;
    while (offset + 1 < length) {
      int value = data.get(offset) & 0xFF;
      if (consecutiveZeros == 3) {
        if (value == 1 && (data.get(offset + 1) & 0x1F) == H264_NAL_UNIT_TYPE_SPS) {
          // Copy from this NAL unit onwards to the start of the buffer.
          ByteBuffer offsetData = data.duplicate();
          offsetData.position(offset - 3);
          offsetData.limit(length);
          data.position(0);
          data.put(offsetData);
          return;
        }
      } else if (value == 0) {
        consecutiveZeros++;
      }
      if (value != 0) {
        consecutiveZeros = 0;
      }
      offset++;
    }
    // Empty the buffer if the SPS NAL unit was not found.
    data.clear();
  }

  /**
   * Returns whether the NAL unit with the specified header contains supplemental enhancement
   * information.
   *
   * @param mimeType The sample MIME type, or {@code null} if unknown.
   * @param nalUnitHeaderFirstByte The first byte of nal_unit().
   * @return Whether the NAL unit with the specified header is an SEI NAL unit. False is returned if
   *     the {@code MimeType} is {@code null}.
   */
  public static boolean isNalUnitSei(@Nullable String mimeType, byte nalUnitHeaderFirstByte) {
    return (MimeTypes.VIDEO_H264.equals(mimeType)
            && (nalUnitHeaderFirstByte & 0x1F) == H264_NAL_UNIT_TYPE_SEI)
        || (MimeTypes.VIDEO_H265.equals(mimeType)
            && ((nalUnitHeaderFirstByte & 0x7E) >> 1) == H265_NAL_UNIT_TYPE_PREFIX_SEI);
  }

  /**
   * Returns the type of the NAL unit in {@code data} that starts at {@code offset}.
   *
   * @param data The data to search.
   * @param offset The start offset of a NAL unit. Must lie between {@code -3} (inclusive) and
   *     {@code data.length - 3} (exclusive).
   * @return The type of the unit.
   */
  public static int getNalUnitType(byte[] data, int offset) {
    return data[offset + 3] & 0x1F;
  }

  /**
   * Returns the type of the H.265 NAL unit in {@code data} that starts at {@code offset}.
   *
   * @param data The data to search.
   * @param offset The start offset of a NAL unit. Must lie between {@code -3} (inclusive) and
   *     {@code data.length - 3} (exclusive).
   * @return The type of the unit.
   */
  public static int getH265NalUnitType(byte[] data, int offset) {
    return (data[offset + 3] & 0x7E) >> 1;
  }

  /**
   * Parses a SPS NAL unit using the syntax defined in ITU-T Recommendation H.264 (2013) subsection
   * 7.3.2.1.1.
   *
   * @param nalData A buffer containing escaped SPS data.
   * @param nalOffset The offset of the NAL unit header in {@code nalData}.
   * @param nalLimit The limit of the NAL unit in {@code nalData}.
   * @return A parsed representation of the SPS data.
   */
  public static SpsData parseSpsNalUnit(byte[] nalData, int nalOffset, int nalLimit) {
    return parseSpsNalUnitPayload(nalData, nalOffset + 1, nalLimit);
  }

  /**
   * Parses a SPS NAL unit payload (excluding the NAL unit header) using the syntax defined in ITU-T
   * Recommendation H.264 (2013) subsection 7.3.2.1.1.
   *
   * @param nalData A buffer containing escaped SPS data.
   * @param nalOffset The offset of the NAL unit payload in {@code nalData}.
   * @param nalLimit The limit of the NAL unit in {@code nalData}.
   * @return A parsed representation of the SPS data.
   */
  public static SpsData parseSpsNalUnitPayload(byte[] nalData, int nalOffset, int nalLimit) {
    ParsableNalUnitBitArray data = new ParsableNalUnitBitArray(nalData, nalOffset, nalLimit);
    int profileIdc = data.readBits(8);
    int constraintsFlagsAndReservedZero2Bits = data.readBits(8);
    int levelIdc = data.readBits(8);
    int seqParameterSetId = data.readUnsignedExpGolombCodedInt();

    int chromaFormatIdc = 1; // Default is 4:2:0
    boolean separateColorPlaneFlag = false;
    int bitDepthLumaMinus8 = 0;
    int bitDepthChromaMinus8 = 0;
    if (profileIdc == 100
        || profileIdc == 110
        || profileIdc == 122
        || profileIdc == 244
        || profileIdc == 44
        || profileIdc == 83
        || profileIdc == 86
        || profileIdc == 118
        || profileIdc == 128
        || profileIdc == 138) {
      chromaFormatIdc = data.readUnsignedExpGolombCodedInt();
      if (chromaFormatIdc == 3) {
        separateColorPlaneFlag = data.readBit();
      }
      bitDepthLumaMinus8 = data.readUnsignedExpGolombCodedInt();
      bitDepthChromaMinus8 = data.readUnsignedExpGolombCodedInt();
      data.skipBit(); // qpprime_y_zero_transform_bypass_flag
      boolean seqScalingMatrixPresentFlag = data.readBit();
      if (seqScalingMatrixPresentFlag) {
        int limit = (chromaFormatIdc != 3) ? 8 : 12;
        for (int i = 0; i < limit; i++) {
          boolean seqScalingListPresentFlag = data.readBit();
          if (seqScalingListPresentFlag) {
            skipScalingList(data, i < 6 ? 16 : 64);
          }
        }
      }
    }

    int frameNumLength = data.readUnsignedExpGolombCodedInt() + 4; // log2_max_frame_num_minus4 + 4
    int picOrderCntType = data.readUnsignedExpGolombCodedInt();
    int picOrderCntLsbLength = 0;
    boolean deltaPicOrderAlwaysZeroFlag = false;
    if (picOrderCntType == 0) {
      // log2_max_pic_order_cnt_lsb_minus4 + 4
      picOrderCntLsbLength = data.readUnsignedExpGolombCodedInt() + 4;
    } else if (picOrderCntType == 1) {
      deltaPicOrderAlwaysZeroFlag = data.readBit(); // delta_pic_order_always_zero_flag
      data.readSignedExpGolombCodedInt(); // offset_for_non_ref_pic
      data.readSignedExpGolombCodedInt(); // offset_for_top_to_bottom_field
      long numRefFramesInPicOrderCntCycle = data.readUnsignedExpGolombCodedInt();
      for (int i = 0; i < numRefFramesInPicOrderCntCycle; i++) {
        data.readUnsignedExpGolombCodedInt(); // offset_for_ref_frame[i]
      }
    }
    int maxNumRefFrames = data.readUnsignedExpGolombCodedInt(); // max_num_ref_frames
    data.skipBit(); // gaps_in_frame_num_value_allowed_flag

    int picWidthInMbs = data.readUnsignedExpGolombCodedInt() + 1;
    int picHeightInMapUnits = data.readUnsignedExpGolombCodedInt() + 1;
    boolean frameMbsOnlyFlag = data.readBit();
    int frameHeightInMbs = (2 - (frameMbsOnlyFlag ? 1 : 0)) * picHeightInMapUnits;
    if (!frameMbsOnlyFlag) {
      data.skipBit(); // mb_adaptive_frame_field_flag
    }

    data.skipBit(); // direct_8x8_inference_flag
    int frameWidth = picWidthInMbs * 16;
    int frameHeight = frameHeightInMbs * 16;
    boolean frameCroppingFlag = data.readBit();
    if (frameCroppingFlag) {
      int frameCropLeftOffset = data.readUnsignedExpGolombCodedInt();
      int frameCropRightOffset = data.readUnsignedExpGolombCodedInt();
      int frameCropTopOffset = data.readUnsignedExpGolombCodedInt();
      int frameCropBottomOffset = data.readUnsignedExpGolombCodedInt();
      int cropUnitX;
      int cropUnitY;
      if (chromaFormatIdc == 0) {
        cropUnitX = 1;
        cropUnitY = 2 - (frameMbsOnlyFlag ? 1 : 0);
      } else {
        int subWidthC = (chromaFormatIdc == 3) ? 1 : 2;
        int subHeightC = (chromaFormatIdc == 1) ? 2 : 1;
        cropUnitX = subWidthC;
        cropUnitY = subHeightC * (2 - (frameMbsOnlyFlag ? 1 : 0));
      }
      frameWidth -= (frameCropLeftOffset + frameCropRightOffset) * cropUnitX;
      frameHeight -= (frameCropTopOffset + frameCropBottomOffset) * cropUnitY;
    }

    @C.ColorSpace int colorSpace = Format.NO_VALUE;
    @C.ColorRange int colorRange = Format.NO_VALUE;
    @C.ColorTransfer int colorTransfer = Format.NO_VALUE;
    float pixelWidthHeightRatio = 1;
    boolean vuiParametersPresentFlag = data.readBit();
    if (vuiParametersPresentFlag) {
      boolean aspectRatioInfoPresentFlag = data.readBit();
      if (aspectRatioInfoPresentFlag) {
        int aspectRatioIdc = data.readBits(8);
        if (aspectRatioIdc == NalUnitUtil.EXTENDED_SAR) {
          int sarWidth = data.readBits(16);
          int sarHeight = data.readBits(16);
          if (sarWidth != 0 && sarHeight != 0) {
            pixelWidthHeightRatio = (float) sarWidth / sarHeight;
          }
        } else if (aspectRatioIdc < NalUnitUtil.ASPECT_RATIO_IDC_VALUES.length) {
          pixelWidthHeightRatio = NalUnitUtil.ASPECT_RATIO_IDC_VALUES[aspectRatioIdc];
        } else {
          Log.w(TAG, "Unexpected aspect_ratio_idc value: " + aspectRatioIdc);
        }
      }
      if (data.readBit()) { // overscan_info_present_flag
        data.skipBit(); // overscan_appropriate_flag
      }
      if (data.readBit()) { // video_signal_type_present_flag
        data.skipBits(3); // video_format
        colorRange =
            data.readBit() ? C.COLOR_RANGE_FULL : C.COLOR_RANGE_LIMITED; // video_full_range_flag
        if (data.readBit()) { // colour_description_present_flag
          int colorPrimaries = data.readBits(8); // colour_primaries
          int transferCharacteristics = data.readBits(8); // transfer_characteristics
          data.skipBits(8); // matrix_coeffs

          colorSpace = ColorInfo.isoColorPrimariesToColorSpace(colorPrimaries);
          colorTransfer =
              ColorInfo.isoTransferCharacteristicsToColorTransfer(transferCharacteristics);
        }
      }
    }

    return new SpsData(
        profileIdc,
        constraintsFlagsAndReservedZero2Bits,
        levelIdc,
        seqParameterSetId,
        maxNumRefFrames,
        frameWidth,
        frameHeight,
        pixelWidthHeightRatio,
        bitDepthLumaMinus8,
        bitDepthChromaMinus8,
        separateColorPlaneFlag,
        frameMbsOnlyFlag,
        frameNumLength,
        picOrderCntType,
        picOrderCntLsbLength,
        deltaPicOrderAlwaysZeroFlag,
        colorSpace,
        colorRange,
        colorTransfer);
  }

  /**
   * Parses a H.265 SPS NAL unit using the syntax defined in ITU-T Recommendation H.265 (2019)
   * subsection 7.3.2.2.1.
   *
   * @param nalData A buffer containing escaped SPS data.
   * @param nalOffset The offset of the NAL unit header in {@code nalData}.
   * @param nalLimit The limit of the NAL unit in {@code nalData}.
   * @return A parsed representation of the SPS data.
   */
  public static H265SpsData parseH265SpsNalUnit(byte[] nalData, int nalOffset, int nalLimit) {
    return parseH265SpsNalUnitPayload(nalData, nalOffset + 2, nalLimit);
  }

  /**
   * Parses a H.265 SPS NAL unit payload (excluding the NAL unit header) using the syntax defined in
   * ITU-T Recommendation H.265 (2019) subsection 7.3.2.2.1.
   *
   * @param nalData A buffer containing escaped SPS data.
   * @param nalOffset The offset of the NAL unit payload in {@code nalData}.
   * @param nalLimit The limit of the NAL unit in {@code nalData}.
   * @return A parsed representation of the SPS data.
   */
  public static H265SpsData parseH265SpsNalUnitPayload(
      byte[] nalData, int nalOffset, int nalLimit) {
    ParsableNalUnitBitArray data = new ParsableNalUnitBitArray(nalData, nalOffset, nalLimit);
    data.skipBits(4); // sps_video_parameter_set_id
    int maxSubLayersMinus1 = data.readBits(3);
    data.skipBit(); // sps_temporal_id_nesting_flag
    int generalProfileSpace = data.readBits(2);
    boolean generalTierFlag = data.readBit();
    int generalProfileIdc = data.readBits(5);
    int generalProfileCompatibilityFlags = 0;
    for (int i = 0; i < 32; i++) {
      if (data.readBit()) {
        generalProfileCompatibilityFlags |= (1 << i);
      }
    }
    int[] constraintBytes = new int[6];
    for (int i = 0; i < constraintBytes.length; ++i) {
      constraintBytes[i] = data.readBits(8);
    }
    int generalLevelIdc = data.readBits(8);
    int toSkip = 0;
    for (int i = 0; i < maxSubLayersMinus1; i++) {
      if (data.readBit()) { // sub_layer_profile_present_flag[i]
        toSkip += 89;
      }
      if (data.readBit()) { // sub_layer_level_present_flag[i]
        toSkip += 8;
      }
    }
    data.skipBits(toSkip);
    if (maxSubLayersMinus1 > 0) {
      data.skipBits(2 * (8 - maxSubLayersMinus1));
    }
    int seqParameterSetId = data.readUnsignedExpGolombCodedInt();
    int chromaFormatIdc = data.readUnsignedExpGolombCodedInt();
    if (chromaFormatIdc == 3) {
      data.skipBit(); // separate_colour_plane_flag
    }
    int frameWidth = data.readUnsignedExpGolombCodedInt();
    int frameHeight = data.readUnsignedExpGolombCodedInt();
    if (data.readBit()) { // conformance_window_flag
      int confWinLeftOffset = data.readUnsignedExpGolombCodedInt();
      int confWinRightOffset = data.readUnsignedExpGolombCodedInt();
      int confWinTopOffset = data.readUnsignedExpGolombCodedInt();
      int confWinBottomOffset = data.readUnsignedExpGolombCodedInt();
      // H.265/HEVC (2014) Table 6-1
      int subWidthC = chromaFormatIdc == 1 || chromaFormatIdc == 2 ? 2 : 1;
      int subHeightC = chromaFormatIdc == 1 ? 2 : 1;
      frameWidth -= subWidthC * (confWinLeftOffset + confWinRightOffset);
      frameHeight -= subHeightC * (confWinTopOffset + confWinBottomOffset);
    }
    int bitDepthLumaMinus8 = data.readUnsignedExpGolombCodedInt();
    int bitDepthChromaMinus8 = data.readUnsignedExpGolombCodedInt();
    int log2MaxPicOrderCntLsbMinus4 = data.readUnsignedExpGolombCodedInt();
    // for (i = sps_sub_layer_ordering_info_present_flag ? 0 : sps_max_sub_layers_minus1; ...)
    for (int i = data.readBit() ? 0 : maxSubLayersMinus1; i <= maxSubLayersMinus1; i++) {
      data.readUnsignedExpGolombCodedInt(); // sps_max_dec_pic_buffering_minus1[i]
      data.readUnsignedExpGolombCodedInt(); // sps_max_num_reorder_pics[i]
      data.readUnsignedExpGolombCodedInt(); // sps_max_latency_increase_plus1[i]
    }
    data.readUnsignedExpGolombCodedInt(); // log2_min_luma_coding_block_size_minus3
    data.readUnsignedExpGolombCodedInt(); // log2_diff_max_min_luma_coding_block_size
    data.readUnsignedExpGolombCodedInt(); // log2_min_luma_transform_block_size_minus2
    data.readUnsignedExpGolombCodedInt(); // log2_diff_max_min_luma_transform_block_size
    data.readUnsignedExpGolombCodedInt(); // max_transform_hierarchy_depth_inter
    data.readUnsignedExpGolombCodedInt(); // max_transform_hierarchy_depth_intra
    // if (scaling_list_enabled_flag) { if (sps_scaling_list_data_present_flag) {...}}
    boolean scalingListEnabled = data.readBit();
    if (scalingListEnabled && data.readBit()) {
      skipH265ScalingList(data);
    }
    data.skipBits(2); // amp_enabled_flag (1), sample_adaptive_offset_enabled_flag (1)
    if (data.readBit()) { // pcm_enabled_flag
      // pcm_sample_bit_depth_luma_minus1 (4), pcm_sample_bit_depth_chroma_minus1 (4)
      data.skipBits(8);
      data.readUnsignedExpGolombCodedInt(); // log2_min_pcm_luma_coding_block_size_minus3
      data.readUnsignedExpGolombCodedInt(); // log2_diff_max_min_pcm_luma_coding_block_size
      data.skipBit(); // pcm_loop_filter_disabled_flag
    }
    skipShortTermReferencePictureSets(data);
    if (data.readBit()) { // long_term_ref_pics_present_flag
      int numLongTermRefPicsSps = data.readUnsignedExpGolombCodedInt();
      for (int i = 0; i < numLongTermRefPicsSps; i++) {
        int ltRefPicPocLsbSpsLength = log2MaxPicOrderCntLsbMinus4 + 4;
        // lt_ref_pic_poc_lsb_sps[i], used_by_curr_pic_lt_sps_flag[i]
        data.skipBits(ltRefPicPocLsbSpsLength + 1);
      }
    }
    data.skipBits(2); // sps_temporal_mvp_enabled_flag, strong_intra_smoothing_enabled_flag
    @C.ColorSpace int colorSpace = Format.NO_VALUE;
    @C.ColorRange int colorRange = Format.NO_VALUE;
    @C.ColorTransfer int colorTransfer = Format.NO_VALUE;
    float pixelWidthHeightRatio = 1;
    if (data.readBit()) { // vui_parameters_present_flag
      if (data.readBit()) { // aspect_ratio_info_present_flag
        int aspectRatioIdc = data.readBits(8);
        if (aspectRatioIdc == NalUnitUtil.EXTENDED_SAR) {
          int sarWidth = data.readBits(16);
          int sarHeight = data.readBits(16);
          if (sarWidth != 0 && sarHeight != 0) {
            pixelWidthHeightRatio = (float) sarWidth / sarHeight;
          }
        } else if (aspectRatioIdc < NalUnitUtil.ASPECT_RATIO_IDC_VALUES.length) {
          pixelWidthHeightRatio = NalUnitUtil.ASPECT_RATIO_IDC_VALUES[aspectRatioIdc];
        } else {
          Log.w(TAG, "Unexpected aspect_ratio_idc value: " + aspectRatioIdc);
        }
      }
      if (data.readBit()) { // overscan_info_present_flag
        data.skipBit(); // overscan_appropriate_flag
      }
      if (data.readBit()) { // video_signal_type_present_flag
        data.skipBits(3); // video_format
        colorRange =
            data.readBit() ? C.COLOR_RANGE_FULL : C.COLOR_RANGE_LIMITED; // video_full_range_flag
        if (data.readBit()) { // colour_description_present_flag
          int colorPrimaries = data.readBits(8); // colour_primaries
          int transferCharacteristics = data.readBits(8); // transfer_characteristics
          data.skipBits(8); // matrix_coeffs

          colorSpace = ColorInfo.isoColorPrimariesToColorSpace(colorPrimaries);
          colorTransfer =
              ColorInfo.isoTransferCharacteristicsToColorTransfer(transferCharacteristics);
        }
      }
      if (data.readBit()) { // chroma_loc_info_present_flag
        data.readUnsignedExpGolombCodedInt(); // chroma_sample_loc_type_top_field
        data.readUnsignedExpGolombCodedInt(); // chroma_sample_loc_type_bottom_field
      }
      data.skipBit(); // neutral_chroma_indication_flag
      if (data.readBit()) { // field_seq_flag
        // field_seq_flag equal to 1 indicates that the coded video sequence conveys pictures that
        // represent fields, which means that frame height is double the picture height.
        frameHeight *= 2;
      }
    }

    return new H265SpsData(
        generalProfileSpace,
        generalTierFlag,
        generalProfileIdc,
        generalProfileCompatibilityFlags,
        chromaFormatIdc,
        bitDepthLumaMinus8,
        bitDepthChromaMinus8,
        constraintBytes,
        generalLevelIdc,
        seqParameterSetId,
        frameWidth,
        frameHeight,
        pixelWidthHeightRatio,
        colorSpace,
        colorRange,
        colorTransfer);
  }

  /**
   * Parses a PPS NAL unit using the syntax defined in ITU-T Recommendation H.264 (2013) subsection
   * 7.3.2.2.
   *
   * @param nalData A buffer containing escaped PPS data.
   * @param nalOffset The offset of the NAL unit header in {@code nalData}.
   * @param nalLimit The limit of the NAL unit in {@code nalData}.
   * @return A parsed representation of the PPS data.
   */
  public static PpsData parsePpsNalUnit(byte[] nalData, int nalOffset, int nalLimit) {
    return parsePpsNalUnitPayload(nalData, nalOffset + 1, nalLimit);
  }

  /**
   * Parses a PPS NAL unit payload (excluding the NAL unit header) using the syntax defined in ITU-T
   * Recommendation H.264 (2013) subsection 7.3.2.2.
   *
   * @param nalData A buffer containing escaped PPS data.
   * @param nalOffset The offset of the NAL unit payload in {@code nalData}.
   * @param nalLimit The limit of the NAL unit in {@code nalData}.
   * @return A parsed representation of the PPS data.
   */
  public static PpsData parsePpsNalUnitPayload(byte[] nalData, int nalOffset, int nalLimit) {
    ParsableNalUnitBitArray data = new ParsableNalUnitBitArray(nalData, nalOffset, nalLimit);
    int picParameterSetId = data.readUnsignedExpGolombCodedInt();
    int seqParameterSetId = data.readUnsignedExpGolombCodedInt();
    data.skipBit(); // entropy_coding_mode_flag
    boolean bottomFieldPicOrderInFramePresentFlag = data.readBit();
    return new PpsData(picParameterSetId, seqParameterSetId, bottomFieldPicOrderInFramePresentFlag);
  }

  /**
   * Finds the first NAL unit in {@code data}.
   *
   * <p>If {@code prefixFlags} is null then the first three bytes of a NAL unit must be entirely
   * contained within the part of the array being searched in order for it to be found.
   *
   * <p>When {@code prefixFlags} is non-null, this method supports finding NAL units whose first
   * four bytes span {@code data} arrays passed to successive calls. To use this feature, pass the
   * same {@code prefixFlags} parameter to successive calls. State maintained in this parameter
   * enables the detection of such NAL units. Note that when using this feature, the return value
   * may be 3, 2 or 1 less than {@code startOffset}, to indicate a NAL unit starting 3, 2 or 1 bytes
   * before the first byte in the current array.
   *
   * @param data The data to search.
   * @param startOffset The offset (inclusive) in the data to start the search.
   * @param endOffset The offset (exclusive) in the data to end the search.
   * @param prefixFlags A boolean array whose first three elements are used to store the state
   *     required to detect NAL units where the NAL unit prefix spans array boundaries. The array
   *     must be at least 3 elements long.
   * @return The offset of the NAL unit, or {@code endOffset} if a NAL unit was not found.
   */
  public static int findNalUnit(
      byte[] data, int startOffset, int endOffset, boolean[] prefixFlags) {
    int length = endOffset - startOffset;

    Assertions.checkState(length >= 0);
    if (length == 0) {
      return endOffset;
    }

    if (prefixFlags[0]) {
      clearPrefixFlags(prefixFlags);
      return startOffset - 3;
    } else if (length > 1 && prefixFlags[1] && data[startOffset] == 1) {
      clearPrefixFlags(prefixFlags);
      return startOffset - 2;
    } else if (length > 2
        && prefixFlags[2]
        && data[startOffset] == 0
        && data[startOffset + 1] == 1) {
      clearPrefixFlags(prefixFlags);
      return startOffset - 1;
    }

    int limit = endOffset - 1;
    // We're looking for the NAL unit start code prefix 0x000001. The value of i tracks the index of
    // the third byte.
    for (int i = startOffset + 2; i < limit; i += 3) {
      if ((data[i] & 0xFE) != 0) {
        // There isn't a NAL prefix here, or at the next two positions. Do nothing and let the
        // loop advance the index by three.
      } else if (data[i - 2] == 0 && data[i - 1] == 0 && data[i] == 1) {
        clearPrefixFlags(prefixFlags);
        return i - 2;
      } else {
        // There isn't a NAL prefix here, but there might be at the next position. We should
        // only skip forward by one. The loop will skip forward by three, so subtract two here.
        i -= 2;
      }
    }

    // True if the last three bytes in the data seen so far are {0,0,1}.
    prefixFlags[0] =
        length > 2
            ? (data[endOffset - 3] == 0 && data[endOffset - 2] == 0 && data[endOffset - 1] == 1)
            : length == 2
                ? (prefixFlags[2] && data[endOffset - 2] == 0 && data[endOffset - 1] == 1)
                : (prefixFlags[1] && data[endOffset - 1] == 1);
    // True if the last two bytes in the data seen so far are {0,0}.
    prefixFlags[1] =
        length > 1
            ? data[endOffset - 2] == 0 && data[endOffset - 1] == 0
            : prefixFlags[2] && data[endOffset - 1] == 0;
    // True if the last byte in the data seen so far is {0}.
    prefixFlags[2] = data[endOffset - 1] == 0;

    return endOffset;
  }

  /**
   * Clears prefix flags, as used by {@link #findNalUnit(byte[], int, int, boolean[])}.
   *
   * @param prefixFlags The flags to clear.
   */
  public static void clearPrefixFlags(boolean[] prefixFlags) {
    prefixFlags[0] = false;
    prefixFlags[1] = false;
    prefixFlags[2] = false;
  }

  private static int findNextUnescapeIndex(byte[] bytes, int offset, int limit) {
    for (int i = offset; i < limit - 2; i++) {
      if (bytes[i] == 0x00 && bytes[i + 1] == 0x00 && bytes[i + 2] == 0x03) {
        return i;
      }
    }
    return limit;
  }

  private static void skipScalingList(ParsableNalUnitBitArray bitArray, int size) {
    int lastScale = 8;
    int nextScale = 8;
    for (int i = 0; i < size; i++) {
      if (nextScale != 0) {
        int deltaScale = bitArray.readSignedExpGolombCodedInt();
        nextScale = (lastScale + deltaScale + 256) % 256;
      }
      lastScale = (nextScale == 0) ? lastScale : nextScale;
    }
  }

  private static void skipH265ScalingList(ParsableNalUnitBitArray bitArray) {
    for (int sizeId = 0; sizeId < 4; sizeId++) {
      for (int matrixId = 0; matrixId < 6; matrixId += sizeId == 3 ? 3 : 1) {
        if (!bitArray.readBit()) { // scaling_list_pred_mode_flag[sizeId][matrixId]
          // scaling_list_pred_matrix_id_delta[sizeId][matrixId]
          bitArray.readUnsignedExpGolombCodedInt();
        } else {
          int coefNum = min(64, 1 << (4 + (sizeId << 1)));
          if (sizeId > 1) {
            // scaling_list_dc_coef_minus8[sizeId - 2][matrixId]
            bitArray.readSignedExpGolombCodedInt();
          }
          for (int i = 0; i < coefNum; i++) {
            bitArray.readSignedExpGolombCodedInt(); // scaling_list_delta_coef
          }
        }
      }
    }
  }

  /**
   * Skips any short term reference picture sets contained in a SPS.
   *
   * <p>Note: The st_ref_pic_set parsing in this method is simplified for the case where they're
   * contained in a SPS, and would need generalizing for use elsewhere.
   */
  private static void skipShortTermReferencePictureSets(ParsableNalUnitBitArray bitArray) {
    int numShortTermRefPicSets = bitArray.readUnsignedExpGolombCodedInt();
    // As this method applies in a SPS, each short term reference picture set only accesses data
    // from the previous one. This is because RefRpsIdx = stRpsIdx - (delta_idx_minus1 + 1), and
    // delta_idx_minus1 is always zero in a SPS. Hence we just keep track of variables from the
    // previous one as we iterate.
    int previousNumNegativePics = C.INDEX_UNSET;
    int previousNumPositivePics = C.INDEX_UNSET;
    int[] previousDeltaPocS0 = new int[0];
    int[] previousDeltaPocS1 = new int[0];
    for (int stRpsIdx = 0; stRpsIdx < numShortTermRefPicSets; stRpsIdx++) {
      int numNegativePics;
      int numPositivePics;
      int[] deltaPocS0;
      int[] deltaPocS1;

      boolean interRefPicSetPredictionFlag = stRpsIdx != 0 && bitArray.readBit();
      if (interRefPicSetPredictionFlag) {
        int previousNumDeltaPocs = previousNumNegativePics + previousNumPositivePics;

        int deltaRpsSign = bitArray.readBit() ? 1 : 0;
        int absDeltaRps = bitArray.readUnsignedExpGolombCodedInt() + 1;
        int deltaRps = (1 - 2 * deltaRpsSign) * absDeltaRps;

        boolean[] useDeltaFlags = new boolean[previousNumDeltaPocs + 1];
        for (int j = 0; j <= previousNumDeltaPocs; j++) {
          if (!bitArray.readBit()) { // used_by_curr_pic_flag[j]
            useDeltaFlags[j] = bitArray.readBit();
          } else {
            // When use_delta_flag[j] is not present, its value is 1.
            useDeltaFlags[j] = true;
          }
        }

        // Derive numNegativePics, numPositivePics, deltaPocS0 and deltaPocS1 as per Rec. ITU-T
        // H.265 v6 (06/2019) Section 7.4.8
        int i = 0;
        deltaPocS0 = new int[previousNumDeltaPocs + 1];
        deltaPocS1 = new int[previousNumDeltaPocs + 1];
        for (int j = previousNumPositivePics - 1; j >= 0; j--) {
          int dPoc = previousDeltaPocS1[j] + deltaRps;
          if (dPoc < 0 && useDeltaFlags[previousNumNegativePics + j]) {
            deltaPocS0[i++] = dPoc;
          }
        }
        if (deltaRps < 0 && useDeltaFlags[previousNumDeltaPocs]) {
          deltaPocS0[i++] = deltaRps;
        }
        for (int j = 0; j < previousNumNegativePics; j++) {
          int dPoc = previousDeltaPocS0[j] + deltaRps;
          if (dPoc < 0 && useDeltaFlags[j]) {
            deltaPocS0[i++] = dPoc;
          }
        }
        numNegativePics = i;
        deltaPocS0 = Arrays.copyOf(deltaPocS0, numNegativePics);

        i = 0;
        for (int j = previousNumNegativePics - 1; j >= 0; j--) {
          int dPoc = previousDeltaPocS0[j] + deltaRps;
          if (dPoc > 0 && useDeltaFlags[j]) {
            deltaPocS1[i++] = dPoc;
          }
        }
        if (deltaRps > 0 && useDeltaFlags[previousNumDeltaPocs]) {
          deltaPocS1[i++] = deltaRps;
        }
        for (int j = 0; j < previousNumPositivePics; j++) {
          int dPoc = previousDeltaPocS1[j] + deltaRps;
          if (dPoc > 0 && useDeltaFlags[previousNumNegativePics + j]) {
            deltaPocS1[i++] = dPoc;
          }
        }
        numPositivePics = i;
        deltaPocS1 = Arrays.copyOf(deltaPocS1, numPositivePics);
      } else {
        numNegativePics = bitArray.readUnsignedExpGolombCodedInt();
        numPositivePics = bitArray.readUnsignedExpGolombCodedInt();
        deltaPocS0 = new int[numNegativePics];
        for (int i = 0; i < numNegativePics; i++) {
          deltaPocS0[i] =
              (i > 0 ? deltaPocS0[i - 1] : 0) - (bitArray.readUnsignedExpGolombCodedInt() + 1);
          bitArray.skipBit(); // used_by_curr_pic_s0_flag[i]
        }
        deltaPocS1 = new int[numPositivePics];
        for (int i = 0; i < numPositivePics; i++) {
          deltaPocS1[i] =
              (i > 0 ? deltaPocS1[i - 1] : 0) + (bitArray.readUnsignedExpGolombCodedInt() + 1);
          bitArray.skipBit(); // used_by_curr_pic_s1_flag[i]
        }
      }
      previousNumNegativePics = numNegativePics;
      previousNumPositivePics = numPositivePics;
      previousDeltaPocS0 = deltaPocS0;
      previousDeltaPocS1 = deltaPocS1;
    }
  }

  private NalUnitUtil() {
    // Prevent instantiation.
  }
}
